Honey bee diet in intensive farmland habitats reveals an unexpectedly high flower richness and a major role of weeds

Abstract

In intensive farmland habitats, pollination of wild flowers and crops may be threatened by the widespread decline of pollinators. The honey bee decline, in particular, appears to result from the combination of multiple stresses, including diseases, pathogens, and pesticides. The reduction of semi-natural habitats is also suspected to entail floral resource scarcity for bees. Yet, the seasonal dynamics and composition of the honey bee diet remains poorly documented to date. In this study, we studied the seasonal contribution of mass-flowering crops (rapeseed and sunflower) vs. other floral resources, as well as the influence of nutritional quality and landscape composition on pollen diet composition over five consecutive years. From April to October, the mass of pollen and nectar collected by honey bees followed a bimodal seasonal trend, marked by a two-month period of low food supply between the two oilseed crop mass-flowerings (ending in May for rapeseed and July for sunflower). Bees collected nectar mainly from crops while pollen came from a wide diversity of herbaceous and woody plant species in semi-natural habitats or from weeds in crops. Weed species constituted the bulk of the honey bee diet between the mass flowering crop periods (up to 40%) and are therefore suspected to play a critical role at this time period. The pollen diet composition was related to the nutritional value of the collected pollen and by the local landscape composition. Our study highlights (1) a food supply depletion period of both pollen and nectar resources during late spring, contemporaneously with the demographic peak of honey bee populations, (2) a high botanical richness of pollen diet, mostly proceeding from trees and weeds, and (3) a pollen diet composition influenced by the local landscape composition. Our results therefore support the Agri-Environmental Schemes intended to promote honey bees and beekeeping sustainability through the enhancement of flower availability in agricultural landscapes.

Consistent pollen nutritional intake drives bumble bee (Bombus impatiens) colony growth and reproduction across different habitats

“…In particular, Valley colonies outperformed Edge and Forest colonies (Table 2), contrary to our expectations that colonies nesting along the field edge would have season‐long diverse pollen resources leading to increased colony growth and reproductive output. This suggests that Valley (agricultural and residential land) colonies may have had easier access to more preferred pollen patches, increasing foraging rates and worker populations in the agricultural habitat, which is consistent with other studies (Requier et al., 2015; Sponsler & Johnson, 2015) indicating that agricultural landscapes—which themselves contain a great deal of edge habitat and weedy plants—can provide abundant and diverse resources for bees. Additionally, proximity to forested land, and perhaps the lower floral diversity in this region, may have led to lower colony growth and reproduction in Forest and Edge habitats (Lanterman & Goodell, 2017).…”

“…In contrast, Valley 4 colonies were placed in wheat and corn fields without any obvious wildflower habitat. Therefore, assessing floral resources in proximity to colonies (Williams et al., 2012) would likely be more predictive of resource diversity, abundance, and quality than assumptions based on general habitat type (Lonsdorf et al., 2009; Requier et al., 2015). …”

“…However, studies examining how variation in landscape influences bee health have focused on managed Apis mellifera honey bees (Otto, Roth, Carlson, & Smart, 2016; Requier et al., 2015; Smart, Pettis, Euliss, & Spivak, 2016; Smart, Pettis, Rice, Browning, & Spivak, 2016; Sponsler & Johnson, 2015). It is therefore not necessarily accurate to extrapolate the results of these studies to solitary bees or bumble bees, which have substantially smaller, annual colonies.…”

Oilseed rape (Brassica napus) as a resource for farmland insect pollinators: quantifying floral traits in conventional varieties and breeding systems

“…However, pollination services in farmed landscapes are threatened, and global declines in insect pollinator abundance and richness (Biesmeijer et al ., 2006; Potts et al ., 2010; Cameron et al ., 2011; Carvalheiro et al ., 2013) have been attributed, in part, to limited quality and availability of food resource, particularly as a result of land use change associated with agricultural intensification (Klein et al ., 2007; Potts et al ., 2010; Goulson et al ., 2015). Recent evidence has revealed the relative paucity of nectar sources in arable farmland compared with seminatural habitats (Baude et al ., 2016) and in such landscapes where alternative food sources are limited, mass‐flowering crops, such as OSR, to create large spatio‐temporal pulses of nectar and pollen that are exploited by wild and managed insect pollinators (Stanley & Stout, 2013; Gill & O'Neal, 2015; Requier et al ., 2015). Cultivation of OSR has been shown to enhance within‐season pollinator abundance (Westphal et al ., 2003; Williams et al ., 2012) and more significantly, between‐year populations (Jauker et al ., 2012; Holzschuh et al ., 2013; Riedinger et al ., 2015).…”

De la concertation territoriale à l'expérimentation en plein champs, différents leviers pour accompagner les acteurs d'un territoire agricole à façonner des paysages durablement favorables à des productions oléagineuses et des productions de miel

“…Entre ces deux floraisons, les abeilles domestiques connaissent une pénurie florale susceptible de contribuer à leur déclin (Requier et al, 2016). Les colonies pour lesquelles cette période de disette est la moins prononcée, s'approvisionnent en pollen auprès de la flore herbacée comme le coquelicot qui peut représenter jusqu'à 60 % de son bol alimentaire pollinique au mois de juin (Requier et al, 2015).…”